1. Technical Field
This disclosure relates to temperature sensors and more particularly to a device adapted to generate an output signal representing the difference between a sensed temperature of an environment and a reference temperature and a related method.
2. Description of the Related Art
CPU for PCs, WORKSTATIONS and SERVERS typically need very sophisticated supply control mechanisms. Their power supplies typically must meet high precision requirements both in stand-by conditions as well as in conditions of load transients. It is known that, in order to reduce costs of the output filter of these systems, “voltage position” techniques, called also “droop function” or “load line regulation”, based on programming the output resistance of the power supply voltage regulator, are often used.
In order to prevent avoidable power dissipations and to sense the output current in a sufficiently refined and continuous manner, the parasitic conduction resistance DCR of the output inductor is typically used as sense resistance.
FIG. 1 depicts a simplified block diagram of a typical three-phase buck voltage regulator 100. The voltage regulator 100 comprises an interleaving oscillator 102 configured to generate mutually out-of-phase ramp signals RAMP1, RAMP2, . . . , RAMPN, and a multiphase pulse-width-modulation (PMW) generator 104 configured to generate mutually out-of phase PMW signals PWM1, PWM2, . . . PWMN. The voltage regulator 100 comprises a plurality of MOS drivers 106 each configured to drive a power MOS output stage 116. Each power MOS output stage 116 is coupled to a supply voltage VIN and a ground and configured to provide a respective current IL1, IL2, . . . ILN through a respective output inductor L1, L2, LN to an output VOUT. The voltage regulator 100 has a capacitor COUT coupled between the output VOUT and the ground.
In these multiphase systems, the output current of the regulator is sensed in order to generate the desired load line. Moreover, information regarding the current flowing through each channel, reference currents IINFO1, IINFO2, . . . IINFON are used to implement the so-called current sharing between the phases of the system and equalizing the currents flowing throughout the phase windings to reduce stresses and damages to components. As illustrated, reference currents IINFO1, IINFO2, . . . IINFON are provided to a current sensing control 114 configured to generate voltage signals VBALANCE—1, VBALANCE—2, . . . VBALANCEN corresponding to the desired reference currents, which are added to an error signal COMP and provided to the multiphase PWM generator 104. An error amplifier 108 is configured to generate the error signal COMP, and is coupled to a reference voltage REF, a current IDROOP proportional to a current supplied to a load, a feed back resistance ZFB 110 and a resistance ZF 112.
The main problem in sensing the current on the conduction resistance DCR of a winding is that its resistance depends on temperature. The temperature coefficient α of copper is about 0.39%, thus even small temperature fluctuations may generate relevant errors in sensing the delivered current.
The voltage read on the winding, for example through TCM (Time Constant Matching) techniques, well known in literature, is as follows:VDCR1=IL·DCR25·[1+α(T−25)]and the current ISENSE read for a single channel is
      I          SENSE      ⁢                          ⁢      1        =            I      L        ·                  DCR        25                    R        G              ·          [              1        +                  α          ⁡                      (                          T              -              25                        )                              ]      being RG the design resistance of the current sensing.
Being
      I    INFO    =            I      L        ·                  DCR        25                    R        G            thenISENSE1=IINFO·[1+α(T−25)]
For temperature compensating N currents, an equal number of thermistors, for example of NTC (Negative Temperature Coefficient) type, would be used. However, because NTC thermistors are relatively expensive, a single NTC sensing for the sum of the currents (IDROOP) is generally performed such to compensate an average temperature of the N phases. In order to do that without using additional pins, the thermistor is introduced in the compensation network, in place of or combined with the feedback resistance ZFB, as shown in FIG. 2, that realizes the so-called droop function.
In FIG. 2, the block MODULATOR indicates generically the PWM signal generator and the drivers of the power stages, the block CURRENT AND THERMAL MONITOR sense the thermally compensated output current and the working temperature, and converts them, for example in digital form, for outputting the reference currents, and the current ISENSE is the sum of the currents of all the phases: IINFO1, IINFO2, . . . IINFON.